Method of forming a molded ring gasket

ABSTRACT

A punch for forming a closure gasket which includes at least two annular grooves, each having a land radially inwardly thereof, a plurality of inwardly extending notches in the lands and extending between the grooves, and generally radially and generally axially facing surfaces disposed outwardly of the grooves for forming a gasket along and inwardly of the skirt portion of a closure. The method includes disposing gasket forming compound on the inner surface of the skirt of a cap shell, moving a punch into a gasket channel of the shell to form a gasket, and allowing air entrapped with the compound to escape radially inwardly of the punch while directing excess gasket compound into a plurality of concentric rings. The closure comprises a cap shell with a gasket having sealing surfaces disposed on the skirt and in a gasket channel just inwardly of the skirt, and excess gasket forming compound disposed in a plurality of rings just inside the channel. The top panel center portion of the closure, and the spaces adjacent the rings, preferably are free of compound or contain not more than relatively thin or intermittent deposits of gasket forming compound.

[451 Sept. 5, 1972 [54] METHOD OF FORMING A MOLDED RING GASKET [72]Inventor: Donald H. Zipper, Western Springs,

[73] Assignee: Continental Can Company,

York, NY.

[22] Filed: June 12, 1969 [21] Appl. No.: 871,109

Related US. Application Data [62] Division of Ser. No. 750,628, Aug. 6,1968,

Pat. No. 3,473,683.

New

[52] US. Cl ..264/268, l8/DIG. 47 [51] Int. Cl ..B29c 13/02 [58] Fieldof Search ..264/268; l8/DIG. 18

[56] References Cited UNITED STATES PATENTS 3,004,298 10/1961 Haynie..18/DIG. 47

FOREIGN PATENTS OR APPLICATIONS Primary Examiner--Robert F. WhiteAssistant Examiner-Richarcl H. Shear Attorney-(heist, Lockwood,Greenawalt & Dewey [57] ABSTRACT A punch for forming a closure gasketwhich includes at least two annular grooves, each having a land radiallyinwardly thereof, a plurality of inwardly extending notches in the landsand extending between the grooves, and generally radially and generallyaxially facing surfaces disposed outwardly of the grooves for forming agasket along and inwardly of the skirt portion of a closure. The methodincludes disposing gasket forming compound on the inner surface of theskirt of a cap shell, moving a punch into a gasket channel of the shellto form a gasket, and allowing air entrapped with the compound to escaperadially inwardly of the punch while directing excess gasket compoundinto a plurality of concentric rings. The closure comprises a cap shellwith a gasket having sealing surfaces disposed on the skirt and in agasket channel just inwardly of the skirt, and excess gasket formingcompound disposed in a plurality of rings just inside the channel. Thetop panel center portion of the closure, and the spaces adjacent therings, preferably are free of compound or contain not more thanrelatively thin or intermittent deposits of gasket forming compound.

4 Claims, 5 Drawing Figures PATENTEDSEP 1912 3,689,625

' INVENTOR L 2 DONALD H. ZIPPER g- BY w be W ATT'YS.

METHOD OF FORMING A MOLDED RING GASKET This application is a division ofapplication Ser. No. 750,628, filed Aug. 6, 1968, now U.S. Pat. No.3,473,683, issued Oct. 21, 1969.

BACKGROUND OF THE INVENTION 1 Field of the Invention The field of theinvention is that of closures with molded sealing gaskets therein, andmethods and ap paratus for making such closures. More particularly, thefield of the invention is that of apparatus and methods formanufacturing closures having plastisol or like gaskets therein,particularly closures which may be pressed onto a threaded jar neck. Inthese closures, subsequent cold flow, reformation or reflow of theplastisol causes the gasket compound to form mating surfaces with thejar neck, thereby forming a closure which is locked in place atop a jarwithout intentional rotation, and which may be removed from the jar onlyby rotation.

More particularly the field is that of jar closures and manufacturingmethods therefor, wherein the amount of gasket-forming or sealingcompound comprising the gasket need not be precisely measured, andwherein the compound need not be disposed in a precise locationwithinthe closure. In these methods, the gasket compound may be spread evenlyover the desired areas of the closure without having excess compoundaccummulate in undesired locations, to cause excessive air entrapment,pockmarks or risk of closure failure, or to present an appearance whichis esthetically undesireable to the consumer.

The field of the invention is also particularly that of apparatus formolding gaskets in which the molding punch or die is arranged tocooperate with the closures shells so as to cause deposition of gasketcompound within the closure shells in particular areas, merely byproperly positioning the punch, and, after deposition of compound,moving the punch axially into position within the closure. For example,the invention is useful in producing improved jar and bottle caps fordiverse end uses, such as hermetic or vacuum sealing of speciallyprepared foods, food products, and the like.

2. Description of the Prior Art Closures such as jar and bottle caps,with which the present invention is concerned, in addition to ordinaryjars or bottles, include those of a type sometimes referred to aspress-on, turn-off caps, described for example, in the Foster et al.U.S. Pat. No. 3,270,904. These caps generally include a top panelportion which is not necessarily desired to be covered with substantialamounts of sealing compound or gasket material. These caps also normallyinclude other interior and exterior protective coatings, a channelportion for receiving that portion of the gasket which is adapted toengage the upwardly or axially facing top seal finish of a containerneck, and a skirt portion which is adapted to receive the inwardlyfacing portion of the gasket which engages the side seal finish of acontainer.

Such closure caps may be made generally according to the method setforth in the Foster et al. Patent. Caps having gaskets withoutsubstantial skirt portions may be made by a method such as thatdescribed in the Owen U.S. Pat. No. 3,360,148. This patent is directedto a method having the objectof eliminating undesirable accummulationsof gasket material on certain surfaces of the cap, and provides forlocalizing such material in single ring or bead inside the principalgasket channel. Caps and methods such as those described in the patentsreferred to above have a number of advantages, and have achievedsignificant commercial success. 1

However, manufacturing experience with such caps has shown that,particularly when a molded gasket is formed which includes a portionextending substantially axially along the skirt as well as into achannel around the outer periphery or margin of the top panel, theamount of compound required is such that the compound must be placed ordeposited along a skirt at a point somewhat spaced apart from thechannel. That is, in the ordinary method of forming a gasket, with thecap in the inverted position, the gasket forming compound must beapplied at a point along the skirt which is spaced upwardly from thechannel.

For example, the Owen Patent shows a cap construction in which thesignificant sealing surface is in the area near the channel whichreceives the sealing compound, and shows that the skirt member does notparticipate in the sealing action. However, in the case of the capsreferred to herein it is desirable to place a gasket therein whichextends a substantial height along the skirt portion, that is, a gasketsuch as that shown in the Foster Patent is desired. Since the compoundis normally deposited in a highly viscous state, it will not immediatelyrun down into the channel or groove. However, since the compound doesrun down to a certain extent, moving a molding punch or die into themolding position tends to entrap air with the compound moving down thesidewall or skirt portion.

The air which is trapped with the compound and swept inwardly as thepunch moves into position remains in or near the compound, and, uponcuring thereof, causes void or pockmarks in the gasket seal area nearthe bottom of the skirt and in the gasket channel of the closure.

With a punch design which allows free movement of air radially inwardlytoward the center of the cap, a

pockmark-free gasket can be made, but two serious drawbacks are presentin such a method. First, the punch must be perfectly centered, andsecond, the amount of compound must be precisely measured and perfectlydistributed so that there is no excess compound present over and abovethat required to form the gasket; otherwise, the excess will be movedinto the center of the cap, forming an irregular mass of compound at arandom position.

Thus, although prior art methods permit rapid and reliable operation,there is still room for improvement in methods and apparatus which willfurther increase operating speed potential, which will decrease thepercentage of rejects or unsatisfactory closures, and which are lesscritical as to accuracy of metering compound into precisely desiredareas, and as to methods of manipulating a forming punch so as to moveit concentrically of a cap at high speeds in order to achieveoutstanding results. Likewise, the prior art has not completely overcomethe disadvantage of entrapped air causing voids or pockmarks in aportion of a gasket which is desired to be used as a sealing surface,particularly in the environment where a gasket is formed which isdisposed along a cap skirt to a substantial extent, as well as withinthe channel portion of such cap.

SUMMARY OF THE INVENTION Accordingly, in view of improvements desired inprior art closures, methods, and apparatus, an object of the presentinvention is to provide an improved cap characterized by outstandingsealing characteristics and an esthetically pleasing appearance.

A further object of the invention is to provide a method ofmanufacturing a closure having gasket surfaces on the skirt portion andon the outer margin of the top panel which includes moving a punchdownwardly into a cap having sealing compound distributed about theskirt, and forcing excess compound and air entrapped therewithcircumferentially within the cap portion, then venting the air andadditional compound radially inwardly, and further directing itcircumferentially to form one or more additional concentric rings ofcompound.

Another object is to provide a cap in which sufficient gasket materialis provided to form the required sealing surfaces, and in which theexcess gasket material is disposed in a uniform and esthetic mannerradially inwardly of the outer edge portions of the cap.

A further object of the invention is to provide a cap which includesgenerally axially and generally radially facing sealing surfaces andwhich includes gasket compound disposed in at least two concentric,spaced apart rings disposed radially inwardly of the outer cap edge.

A still further object of the invention is to provide a method ofdistributing sealing compound within the shell of a cap member to form agasket closure which includes the steps of bleeding or venting entrappedair radially inwardly of the closure, and simultaneously directingexcess compound into two or more circumferentially extending rings.

A still further object of the invention is to provide a molding punchwhich includes axially and radially facing surfaces for forming .agasket within a closure member, a plurality of lands defining concentricgrooves, notches in the lands for venting air between grooves, and inwhich the grooves serve to distribute the sealing compound intocircumferentially extending, concentric rings inside a jar or the like.

The present invention achieves these objects, and other objects inherenttherein, by providing a closure with a top panel, an outer marginportion and a skirt depending therefrom, and a sealing gasket adhered toand disposed inside the skirt and margin portion, in which excess gasketcompound is formed into a plurality of concentrically disposed ringsinside the outer margin, the rings being spaced apart from each otherand having webs of gasket forming compound extending therebetween. Theinvention also achieves its objects by providing a method and apparatusfor venting excess sealing compound and air entrapped therewith radiallyinwardly of the gasket of surfaces by providing a series of notchedgrooves which allow escape or venting of excess sealing compound fromthe channel and direct it into a plurality of concentric rings.

The exact manner in which this invention achieves its objects, andothers which are inherent therein, will become more apparent whenconsidered in conjunction with the following detailed description of theBRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view ofa cap shell disposed in an inverted position with gasket formingdeposited therein before forming or shaping the gasket member;

FIG. 2 is a plan view of the inner surface of a gasketed closure madeaccording to the present invention;

FIG. 3 is a vertical sectional view, with portions broken away, takenalong lines 33 of FIG. 2, showing the moving punch forming the gasket inthe closure;

FIG. 4 is a vertical sectional view, taken along lines 44 of FIG. 2,showing a different aspect of the molding punch in position within thecap shell unit;

FIG. 5 is a plan view, with portions broken away, showing the axial endface of the molding punch of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Although itwill be understood that the present invention may be practiced in anumber of forms, the invention will be described by reference to agasketed cap or closure assembly adapted to be pressed onto a jar orbottle, such as a baby food jar, without intentional rotation thereof,and adapted to be removed therefrom by twisting motion. However, theinvention is useful with other types of caps and closures, which will beappreciated by those skilled in the art. It will be understood, inreference to the detailed description, that it is customary to form thegasket placed within the closure when the closure is in a position ofuse which is inverted with respect to its normal position on top of acontainer. That is, during manufacture, the top panel is disposeddownwardly and the skirt portion extends upwardly therefrom, whereas, inuse, the top panel of the cap has the skirt extending downwardlytherefrom.

Referring now to the drawings in greater detail, FIG. 1 shows theclosure unit 20 after formation of the exterior metal cap portion 22,but before the gasket forming sealing compound 24 is in a desiredconfiguration, and before molding thereof. The metal cap comprises anend panel 26, which may include a partially domed center or button 28,which may be adapted to display the condition of vacuum or pressurewhich is within the container, a circumferentially extending channel 30container one or more re-entrants 32, and a skirt portion 34 whichterminates in a rolled bead portion 36. An axially offset flange orshoulder 38, in combination with the skirt 34, defines the channel 30,which may be considered as an outer margin of the end panel 26. There-entrant 34 is preferred but not necessary to the in vention. Thechannel 30 is thus axially offset from the principal surface of the capportion 26, so the compound 24 forming the gasket may be confinedtherein.

As shown in FIG. 1, the cap is disposed in position with the innersurface thereof extending upwardly, with compound 24 disposed. in agenerally uniform ring or bead along the skirt portion 34 of the cap.The method of depositing this compound is well known in the art, andtypically consists of injecting unflexed plastisol or other fluentgasket forming material 24 through a nozzle directed at the skirt 34while rotating the cap member 22 on a turn-table, typically at a speedof 500 to 1,500 rpm. After the compound 24 is deposited, it is formedinto the desired shape by forming it with a molding punch 40, such asthat shown in FIG. 3.

This punch 40 has a radially outwardly facing, large diameter guidesurface 42, a step 44 therein, and a generally inwardly tapering,reduced diameter circumferentially extending wall portion 46. Roundedcorner 48 joins the reduced diameter wall portion 46 to a generallyaxially facing surface 50, which forms a sealing surface in the compound24 which will engage the top seal finish of the container. Radiallyinwardly of the axially facing surface 50 is a step portion 52, and,disposed radially inwardly thereof are a radially outer land 54, aradially outer groove 56, an intermediate land 58, an inner groove 60,and an innermost land 62, respectively. The innermost land 62 terminatesat a generally cylindrical wall 64, which extends axially upwardlytherefrom, leaving an opening 66 in the center portion of the punch 40.

Referring to FIGS. 4 and 5, it is shown that the intermediate land 58and the inner land 62 include notches 68, 70 respectively associatedtherewith, the notches 68 preferably being of lesser depth or heightthan the radially more inwardly disposed notches 70.

Referring to FIGS. 2, 3 and 4, the configuration of the gasket material24 is shown in the form finally assumed after the punch 40 has completedits downward movement within the cap 22. The shaped gasket comprises askirt portion 72, which faces generally radially inwardly to form onesealing surface for engaging a side seal finish, and a generally axiallyfacing, surface 74 for engaging the top seal finish of a container.Radially inwardly of the axially facing surface 74 is a very thinsection 76 of gasket material. Further inwardly thereof is a first beador ring 78, a second thin coating 80, and an inner bead or ring 82. t

The thin sections 76, 80 are normally of a thickness of from about 0.001to 0.005 inch, preferably 0.002 inch. The significance of thesedimensions will be discussed later. Between the grooves 54, 58, andinwardly of the groove 58 are outer webs 84 and inner webs 86respectively of gasket material, which are formed where the plastisolmaterial moves radially in the grooves 68, 70. Normally, the thicknessof the webs 84, 86 is about 0.010 up to about 0.030 inch. The inner land62 preferably contacts or comes within 0002 or less of contacting theinner surface of the cap member 22. The second or inner web 86 extendsradially inwardly of the ring 82, but this web 86 and the ring portionsimmediately adjacent the web 86 are only formed in the event thatsufficient compound is forced through the notch 68 to causecircumferential flow in the groove 60. Thus, the inner ring 82 isnormally of intermittent or fragmentary extent, with the webs 86 beingpresent where the ring 82 has attained full thickness or height. Theextent of the ring 82 is also determined by the amount of compound used,and the disposition thereof.

Referring now to the operation of the process as the punch movesdownwardly into the caps, when the punch 40 moves axially downwardlyinto the cap 22, the mass of sealing compound 24 is engaged by the wall46 of the punch. A portion of the material is forced somewhat upwardlynear the bead 36 of the cap and the remainder is forced downwardly 'intothe channel 30 which forms the radially outer surface portion of the toppanel 26. When the channel 30 is completely filled, excess compoundtends to be forced inwardly, over the step 52 and into the groove 56.The material forced beneath the land 58 is either a rather viscousplastisol or like material, or entrapped air. If it is air, it proceedsfreely radially inwardly of the punch, and is vented at the centerthereof. If it is a plastisol material, the attempted passage beneaththe land 58 is restricted, not only because of the narrow space betweenthe land 58 and the inner surface of the cap 22, but because theplastisol therein may, for example, in the case of a heated punch, tendto solidify earlier than the remaining mass thereof. Thus, the excessplastisol moves radially at an extremely limited rate, or not at all,inwardly until the groove 56 is substantially full. However, in moving,the plastisol flowing circumferentially encounters the spaced apartnotches 68 in the land 58, where relatively few passage is permitted byreason of the increased cross-sectional area of the passage thus formed.Material flowing through the notch 68, if present in sufficient quantityis substantially unable to pass beneath the innermost land 62, which iseither in contact with or very closely spaced apart from the flat,inwardly directed surface 26 of the cap 22. Since plastisol can not flowradially inwardly because of the restriction imposed by the land 58, itis again directed into the second or inner groove in a circumferentialdirection.

If there is more than enough plastisol to fill or substantially fill theinner groove 60, the excess is then vented, together with any airtrapped therewith, radially inwardly through the second set of notches70. Excess compound may form a plurality of second, generally radiallyinwardly extending spokes or webs 86, such as those shown in FIG. 2. Infurther reference to FIG. 2, it will be noted that a condition isillustrated wherein there was somewhat more excess compound from theleft side of the cap than on the right side, as a result of which webs86 were formed extending general inwardly of the cap, whereas, referringto the right hand side of FIG. 2 it is shown that the inner webs 86 arediscontinuous and fragmentary, and that the inner ring 82 is of asmaller cross section, or fragmentary or incomplete. Although the gasketnormally is quite symmetrical, gaskets lacking perfect symmetry due touneven disposition of compound are still satisfactory, since in suchcase, the present method distributes the compound in a satisfactorymanner, as shown. Some excess compound is always provided to assurecomplete filling and to prevent voids or pockmarks.

Although the size of the dimensions and exact structural features of theinvention are not of critical importance, it is preferred that theoutward set of notches 68 be somewhat smaller than the inner set ofnotches 70, and that the land 58 be spaced apart from the inner surfaceof the cap, in position of use, a distance somewhat greater than thespacing between the inner land 62 and the inner face of the cap 22.

The contour of the cap shown, particularly that of the channel 30, there-entrant 32, and the exact shape or size of the skirt portion 34 arenot of critical importance, and may be varied in the manner known tothose skilled in the art. The contour of the punch is made after the capcontour or profile is determined so as to provide for the propercap-to-land clearances.

Preferably, the gasket compound is in a moldable form, and, in the caseof a plastisol, the vinyl resin is insoluble in the plasticizer atambient temperature. The viscosity of the material is very high, and itwill retain the shape it assumes after being placed in the shell, atleast until the molding is initiated by moving the punch 40 intoposition. The punch may be a heated punch having a temperature of fromabout 250 to 400 F. Moving the punch into contact with the plasticizerserves to impart sufficient cure thereto, so that it will retain itsshape, although not actually fully cured. A final cure of one to fiveminutes in a heated dryer or oven of 300 to 400 F. will typically besufficient to finish curing the resin in place. In the event a foamableplastisol or other foamable composition is used, it may be cured in asimilar manner, or in any other manner known to those skilled in theart. Thus, although the process of the invention normally includes oneor more curing or post-curing steps, the exact material used, or themethod of curing it does not form an essential aspect of the invention.

One of the principal advantages of the closure made according to thepresent invention is that excess compound is kept from randomlyextending across the inner surface of the cap, and the rings impart aneat, geometric and esthetically pleasing appearance to the inside ofthe cap, while assuring that all air is vented from beneath the punch toavoid pockmarks or voids in the gasket. Thus, a combination of higherquality, greater latitude in dimensional and quantitative tolerances,and better appearance are made possible. Another advantage is that, byconstructing a molding punch according to the invention, movement of thepunch into the cap into a known manner, inherently performs the severalmanipulative steps of the process substantially simultaneously, withonly one axial movement or operation. The simplicity of the methodcontributes to its economy and reliability, and fewer inferior or rejectcaps are made. I

The spacing of the lands from the inner surface of the cap with thedimensions given herein is desired, since it is desired that theoutermost groove provide substantial resistance to flow radiallyinwardly therefrom, whereas the same degree restriction is not neededradially inwardly of the inner groove. Thus, for a typical cap, thenotch 68 may be 0.002 inch deep with respect to the land 58, whereas thenotch 70 is preferably 0.005 inch deep with respect to the land 62.Staggering or circumferentially offsetting the notches 68, 70 from eachother aids in the sequence of filling the grooves and notches to formthe rings and webs in the closures of the present invention, andprevents uncontrolled or random forcing of compound into the center ofthe top panel 28.

Suitable sealing compounds for use with the invention are well known tothose skilled in the art, and are,

. 8 I for example, of the types referred to in the Foster et al. US.Pat. No. 3,270,904, the Owen US. Pat. No. 3,360,148, and in patentsreferred to therein.

It will thus be seen that the present invention provides a novel asketedclosure, formin punch, and molding metho having a number of a vantagesand characteristics including those hereinbefore pointed out, and otherswhich are inherent in the invention.

lclaim:

1. A method of fonning a gasket in a shell element to form a gasketedclosure unit, said method comprising disposing a ring of an at leastpartially fluent gasket forming compound along an inner surface of theskirt portion of a shell element, forcing said compound along said skirtportion and at least partially radially inwardly toward an outer marginportion of the top panel portion of said shell, fully filling said outermargin portion with said compound, and, whileallowing air entrapped withsaid compound to escape both radially inwardly and circumferentially ofsaid outermargin portion, forcing a portion of excess compoundcircumferentially of said outer margin portion by preventingsubstantial, radially inward free flow of said compound, thereafterallowing limited radial flow of compound, and again forcing a portion ofsaid compound circumferentially before allowing free radially inwardmovement thereof, whereupon entrapped air is vented, and excess compoundforms at least portions of two circumferential rings radially inwardlyof said outer margin portion of said shell element.

2. A method as defined in claim 1 in which allowing air entrapped withsaid compound to escape includes the step of moving compound flowrestricting means closely adjacent said top panel portion of said shella distance such that air may escape through said distance, but whereinsealing compound tending to flow therethrough is substantiallysolidified and will not flow therethrough.

3. A method of simultaneously forming a gasket in a shell member toproduce a gasketed closure unit and venting air entrapped with a mass ofgasket-forming compound disposed on the skirt portion and a radiallyouter margin of the top panel portion of said shell member, said methodcomprising first moving a molding punch into a closely overlyingrelation to said mass of material, preventing free radially inward flowof material by surrounding a periphery of said material with a pluralityof lands containing venting notches therein and forming a plurality ofconcentric, circular grooves, further axially moving said punch to aposition wherein said lands substantially engage the inner surface ofsaid top panel, whereby air may be vented from between said lands andsaid inner surface, and said compound and additional air may passthrough said notches, while said compound is forced circumferentially insaid grooves between said notches.

4. A method as defined in claim 3 in which said venting notches in theoutermost land are of a lesser depth than said venting notches in theinnermost land.

1. A method of forming a gasket in a shell element to form a gasketedclosure unit, said method comprising disposing a ring of an at leastpartially fluent gasket forming compound along an inner surface of theskirt portion of a shell element, forcing said compound along said skirtportion and at least partially radially inwardly toward an outer marginportion of the top panel portion of said shell, fully filling said outermargin portion with said compound, and, while allowing air entrappedwith said compound to escape both radially inwardly andcircumferentially of said outer margin portion, forcing a portion ofexcess compound circumferentially of said outer margin portion bypreventing substantial, radially inward free flow of said compound,thereafter allowing limited radial flow of compound, and again forcing aportion of said compound circumferentially before allowing free radiallyinward movement thereof, whereupon entrapped air is vented, and excesscompound forms at least portions of two circumferential rings radiallyinwardly of said outer margin portion of said shell element.
 2. A methodas defined in claim 1 in which allowing air entrapped with said compoundto escape includes the step of moving compound flow restricting meansclosely adjacent said top panel portion of said shell a distance suchthat air may escape through said distance, but wherein sealing compoundtending to flow therethrough is substantially solidified and will notflow therethrough.
 3. A method of simultaneously forming a gasket in ashell member to produce a gasketed closure unit and venting airentrapped with a mass of gasket-forming compound disposed on the skirtportion and a radially outer margin of the top panel portion of saidshell member, said method comprising first moving a molding punch into aclosely overlying relation to said mass of material, preventing freeradially inward flow of material by surrounding a periphery of saidmaterial with a plurality of lands containing venting notches thereinand forming a plurality of concentric, circular grooves, further axiallymoving said punch to a position wherein said lands substantially engagethe inner surface of said top panel, whereby air may be vented frombetween said lands and said inner surface, and said compound andadditional air may pass through said notches, while said compound isforced circumferentially in said grooves between said notches.
 4. Amethod as defined in claim 3 in which said venting notches in theoUtermost land are of a lesser depth than said venting notches in theinnermost land.